The present invention relates to empty-load changeover apparatus and more specifically, to a combined empty-load changeover and load-sensing and proportioning device.
An empty-load changeover apparatus currently in use as a changeover device mounted to pipe bracket and a separate load-sensing mechanism is shown in U.S. Pat. No. 3,671,086 to Scott and generally known as an SC-1 valve. This apparatus is much too large and heavy to be mounted on a railroad truck. U.S. Pat. No. 4,653,812 to Engle discloses a combined empty-load changeover and load-sensing device capable of being mounted to a railroad truck, but is also much too large and heavy. A much lighter and more compact empty-load valve device is shown in U.S. Pat. No. 4,844,554 to Rojecki. Although Rojecki was an improvement over the prior art, it was a specialty valve.
Thus, it is an object of the present invention to provide an empty-load device which has a minimum piping requirement and uses more standard parts.
Another object of the present invention is to provide an empty-load device which protects against erroneous and false indication of car loading by movement of the load-sensing arm caused by rock and roll of the car.
These other objects are achieved by an empty-load device having a single housing, which includes a brake cylinder, control valve, and equalizing valve ports. A sensing piston and ratio piston are interconnected by a push rod which selectively controls the fluid pressure at the brake cylinder port in accordance with sense load force. A ratio valve bypasses the ratio piston and in combination limits the fluid pressure at the brake cylinder port. The improvement of the structure includes the ratio valve being mounted on and travelling with the ratio piston. The push rod engages and maintains the ratio valve open except for empty sensed load force. The ratio valve is a check valve including a valve seat in the ratio piston, a valving element, a spring cage, and a valve spring in the ratio piston. The ratio piston and the sensing piston face each other, and the brake cylinder port lies therebetween. The ratio valve is on the opposite and smaller surface of the ratio piston.
The push rod, which engages the ratio valve, in combination with the valve spring and spring cage maintains the ratio piston against a first stop in the housing for brake release and for a loaded sensed load force. The ratio piston disengages the first stop for an empty sensed load force and the push rod engages the valving element and positions the ratio piston for variations of the empty sensed load force. The ratio piston is also repositioned by differential pressure across the ratio valve for an empty sense load force.
The equalization port is disconnected from the control valve port and connected to an exhaust port when the ratio piston engage the first stop and is connected to the control valve port and disconnected from the exhaust port when the ratio piston disengages from the first stop.
The unique relationship of the push rod with the spring loaded ratio valve mounted in the ratio piston provides protection from the false indication of ca loading by variations from the normal loaded and empty load positions of the sensing arm caused by rock and roll.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.